Surface Landmarks and Bony Projections

Surface landmarks and bony projections are the palpable or visible reference points used to locate internal structures and to orient an image to the body. On the skin they include features such as the suprasternal notch, the iliac crests, or the umbilicus; on the skeleton they include processes, tubercles, lines, and joint margins that are stable enough to anchor localisation and measurement.

Definition

Anatomic landmarks are identifiable, relatively constant structures of the body surface or skeleton used as reference points to locate other structures, define imaging levels and planes, and standardise measurements.

Scope

This topic covers the identifiable reference points used to navigate anatomy on imaging: external surface landmarks, the bony projections and margins seen on radiographs and cross-sectional images, and named cortical or organ-surface features used in finer parcellation. It addresses how such landmarks support localisation, slice-level identification, and reproducible measurement. It is a reference entry, not a procedural guide.

Core questions

• Which surface and bony features are stable enough to serve as reference points?
• How do landmarks define imaging levels, planes, and lines of measurement?
• How are landmark-based descriptions translated between body surface, skeleton, and cross-sectional images?

Key concepts

• Surface (cutaneous) landmarks
• Bony processes, tubercles, and margins
• Vertebral levels as a localisation reference
• Reference lines and planes
• Cortical sulci and gyri as neuroanatomical landmarks
• Reproducibility of landmark-based measurement

Mechanisms

Landmarks work because certain structures occupy a relatively constant position and have a recognisable shape, so they can be located reliably across people and re-identified across images. A reader uses them in two directions: from the surface inward (for example, palpating a bony point to estimate the level of a deeper structure) and within the image itself (using a bony margin or a named sulcus to fix a slice level or to standardise where a measurement is taken). On cross-sectional brain imaging, named sulci and gyri serve as fine-grained landmarks that automated systems can parcellate against a standard nomenclature.

Clinical relevance

Stable surface and bony landmarks let a reader name where a finding lies, identify the level of a slice, and place measurements consistently so they can be repeated and compared. Because they are relatively fixed, they also help flag when a structure is displaced from its expected position. This entry describes localisation practice and is not guidance for any individual procedure or diagnosis.

Evidence & guidelines

Landmark use is grounded in descriptive anatomy and standardized nomenclature rather than trial evidence; modern neuroimaging adds reproducible, atlas-referenced parcellation of cortical landmarks, while reviews of imaging pitfalls underline that a landmark's usefulness depends on recognising its normal variability.

History

Surface and bony landmarks are among the oldest tools of clinical anatomy, used long before imaging to estimate the position of deep structures. Plain radiography then made bony projections the primary in-image references, and cross-sectional imaging extended the idea to internal soft-tissue and cortical landmarks, which automated parcellation methods now identify against standard anatomical nomenclature.

Key figures

• Jean Talairach
• Bruce Fischl
• Christophe Destrieux

Seminal works

• destrieux-2010
• talairach-tournoux-1988

Frequently asked questions

What is the difference between a surface landmark and a bony projection?

A surface landmark is a feature identifiable on the body surface (such as the suprasternal notch or an iliac crest), while a bony projection is a skeletal feature (such as a process or tubercle) seen directly on imaging. Both serve as reference points, but bony projections are imaged directly whereas surface landmarks are often used to estimate the level of deeper structures.

Why are sulci and gyri called landmarks in brain imaging?

Major sulci and gyri occupy relatively consistent positions and have recognisable shapes, so they act as reference points for localising cortical regions and for parcellating the cortex against a standard anatomical nomenclature.